There are several methods available to separate and purify molecules in a solution. Several different complementary chromatographic techniques are often used serially, e.g. gel filtration, ion exchange chromatography, hydrophobic interaction chromatography and bioaffinity chromatography. The use of several chromatographic steps is cumbersome and can be costly particularly when working at a micro scale.
Magnetic beads are used for diverse purposes such as isolating nucleic acids and proteins as well as viruses and whole cells. The most commonly used magnetic bead is that which is used in combination with attached ligands which have an affinity for different substances.
EP0221046 (Monsanto Company) describes pore surfaces in membranes/matrices that can be coated with polymers of such molecular weight that clogging of the pores is prevented.
U.S. Pat. No. 5,834,121 (Sucholeiki et al.) describes a composite magnetic bead and a method of making a composite magnetic bead. The polymer coated metal oxide particles are encapsulated in a rigid and solvent stable polymer of vinyl monomers in order to retain the metal oxide particles during harsh conditions. The primary beads are enclosed in a micro porous polymer bead which is capable of swelling in organic solvents and allowing for further functionalization in order to be useful for organic synthesis. The procedure aims to produce a hydrophobic bead.
U.S. Pat. No. 6,204,033 (Muller-Schulte) describes the preparation of polyvinyl alcohol-based magnetic beads for binding biomolecules. The spherically shaped polyvinyl alcohol polymer particles are prepared encapsulating a magnetic colloid. The beads are particularly suited to use in cell separation/sorting, cleaning biosubstances in suspension and diagnostic assays. The polymer particles contain reactive hydroxyl groups and can be provided with spacer molecules to which biomolecules can bind.
U.S. Pat. No. 6,274,387 (Yamauchi et al.) describes a magnetic carrier, preparation thereof, and a method of extraction of nucleic acid. The magnetic carrier comprises particulate silica containing a magnetic material, having a polyacrylamide on the surface.
EP 0179039 (Exploaterings AB T.B.F) describes a particle consisting of a solid core with a surface containing immobilised metal ions and surface coated with a polymer used for the separation of biomolecules. This reference is based on the ability of metals and metal ions to combine with a polymer that has been substituted with a metal chelate builder, in addition they contain an excess of hydroxyl groups which can be used for coupling biologically active components.
U.S. Pat. No. 7,897,257 (Alterman et al.) describes a bead with an inner core of magnetic particles, which are coated in an inert synthetic polymer and then enclosed in a hydrophilic porous polymer, preferably agarose. The applications of the magnetic bead include use for cell cultivation and chromatography. Use in chromatography would require that the agarose layer is provided with ligands that have an affinity for a specific biomolecule. Superdex®, marketed by GE Healthcare Lifesciences, is a porous particles of cross linked agarose coated with dextran on the exterior and the interior.
While several magnetic beads have been previously described there is a need for a small scale (a volume less than 10 L), simple and cost effective method of separating chemicals.